An image forming apparatus utilizing a digital technology, for example, an electronic copying machine, has a fixing apparatus for fixing a developer image molten by heating onto paper by applying a pressure to the image.
Such a fixing apparatus comprises: a heating member for melting a developer, for example, a toner, and a pressurizing member for applying a pressure to the heating member, wherein a predetermined contact width (nip width) is formed in a contact region (nip portion) between the heating member and the pressurizing member. The developer on the paper passing through the nip portion is molten by a heat from the heating member, the molten developer is pressurized by the pressurizing member to be fixed onto the paper. In recent years, a heating device utilizing inductive heating has been utilized in this fixing apparatus. For example, there is known a heating device for generating a magnetic field from a coil, and then, supplying an eddy current to a thin film conductive layer formed outside of the heating member, thereby generating a heat.
The heating member includes a roller shaped elastic member inside of the conductive layer in order to ensure a predetermined or greater nip width between the heating member and the pressurizing member. The elastic member is composed of, for example, a foam rubber or the like, and includes a large amount of air. Thus, the elastic member has a large thermal expansion coefficient. On the other hand, the conductive layer including a metal or the like has a thermal expansion coefficient which is smaller than that of the elastic member. Thus, the expanded elastic member pushes the conductive layer from the inside, and the hardness of the heating member becomes high. Therefore, there is a problem that a predetermined or greater nip width cannot be allocated.